1. Field of the Invention
The present invention relates to touch panels with low cost.
2. Description of Related Art
Touch panels incorporated with touch control and display technologies are widely used in electronic devices, such as cellular phones, digital cameras, computers, and so on. The user interface of such devices not only presents visual information but also allows the user to perform operations.
Touch panels can be divided into on cell touch panels and in cell touch panels. The on cell touch panels include a touch screen and a display, in which the former comprises touch sensors constructed by transparent patterns and the latter may be a liquid crystal display. The in cell touch panels integrate the touch sensors or photo sensors into the pixels of the liquid crystal display.
Because the manufacturing steps are increased, the cost of the on cell touch panels is higher than that of the in cell touch panels. FIG. 1 and FIG. 2 show the causes of high manufacturing cost, in which FIG. 1 is a cross-section of a fringe field switching mode liquid crystal display (FFS LCD) and FIG. 2 is a cross-section showing a touch screen formed on the FFS LCD.
Referring to FIG. 1, the FFS LCD primarily includes a lower substrate 10, an upper substrate 20, and a liquid crystal layer 30 arranged between the two substrates 10/20. In addition, a counter electrode 11 is arranged on the inner surface of the lower substrate 10, a gate insulation layer 12 is arranged on the counter electrode 11, pixel electrodes 13 are arranged on the gate insulation layer 12, and an alignment layer 14 covers the pixel electrodes 13. The counter electrode 11 and the pixel electrodes 13 are typically made of transparent conductive materials, such as indium tin oxide (ITO); they are employed for driving the liquid crystal layer 30, and the distance between the counter electrode 11 and the pixel electrodes 13 is less than the distance between the upper substrate 20 and the lower substrate 10. Besides, the lower substrate 10 further includes gate lines (not shown) and data lines (not shown) orthogonally arranged with each other to define the pixels, and thin-film transistors are arranged near the intersections of the data lines and gate lines.
Furthermore, black matrixes 21 are formed below the inner surface of the upper substrate 20. Color filters 22, including red (R), green (G), and blue (B) filters, are arranged between the black matrixes 21. An over coating layer 23 is arranged below the black matrixes 21 and the color filters 22 for protecting the color filters 22 and flattening the surface. An alignment layer 24 is formed below the over coating layer 23. In addition, polarizing plates may be respectively arranged on the outer surface of the upper substrate 20 and below the outer surface of the lower substrate 10.
When different voltages are respectively supplied to the counter electrode 11 and the pixel electrodes 13, a fringe filed is thus generated to drive the liquid crystal layer 30. Because both two driving electrodes 11/13 are arranged at the side of the lower substrate 10, the touch panel may suffer from electrostatic issues. To overcome this problem, a transparent conductive layer 25, such as indium tin oxide, is arranged on the outer surface of the upper substrate 20 as an electrostatic protection layer 25.
Referring to FIG. 2, an insulation layer 40 or an over coating layer 40 has to be formed to isolate the transparent conductive layer 25 before forming touch sensors. After that, a transparent conductive layer 41, an insulation layer 42, a transparent conductive layer 43, a protective layer 44, and so on are formed on the over coating layer 40, for forming the touch sensors.
It is clear that the increased layers will increase the manufacturing steps and the material cost, resulting in low yield and high cost. Therefore, it would be advantageous to provide a novel touch panel with low cost.